Retatrutide - the next-generation weight loss medication

Retatrutide is the medication a lot of patients have started asking about by name. It is the next-generation weight-loss treatment from Eli Lilly, the same manufacturer behind Mounjaro. It is not yet available in the UK. If and when it is licensed by the MHRA, it will be on the LoveMyLife formulary on day one.

This article explains what retatrutide actually is, why the early evidence has the obesity-medicine world paying close attention, and what to make of the regulatory journey ahead.

What makes retatrutide different

Wegovy contains semaglutide, a single-hormone agonist that mimics GLP-1. Mounjaro contains tirzepatide, a dual agonist that mimics GLP-1 and GIP. Retatrutide is the next step in this sequence: a triple-hormone agonist that activates GLP-1, GIP, and a third receptor, glucagon.

Adding glucagon-receptor activity is the genuinely new piece. Glucagon is best known as the hormone that raises blood sugar, but at the doses retatrutide reaches it has been shown to do something else clinically useful: it nudges energy expenditure upwards. In plain terms, the body burns slightly more fuel at rest. Combine that with the appetite-quieting GLP-1 effect and the metabolic-efficiency GIP effect, and the three actions stack on top of each other.

This is the first weight-loss medication where the mechanism is not only "eat less" but also a small amount of "burn more". On paper it should produce greater weight loss than the dual-agonist approach. The trial data so far suggest it does.

What the trial data shows

The Phase 3 TRIUMPH-1 trial reported topline results on 21 May 2026. The key numbers:

Participants on the 12mg weekly dose lost an average of 28.3 percent of their starting body weight over 80 weeks.

Participants with a starting BMI of 35 or higher who continued on the medication lost up to 30.3 percent at 104 weeks.

Weight loss continued past the point where injectable semaglutide and tirzepatide tend to plateau, with a curve that had not fully levelled off at the end of the trial.

For context: the best-case figures for currently licensed medication are roughly 15 percent (Wegovy 2.4mg), 20.7 percent (Wegovy 7.2mg) and 22.5 percent (Mounjaro 15mg). Retatrutide's headline number is meaningfully higher.

There were also signals beyond weight loss. A separate Phase 3 trial reported significant pain relief in osteoarthritis. Cardiovascular outcomes and type 2 diabetes data are reading out through the rest of 2026. The package is shaping up as more than just a weight-loss number.

What we still need to learn

The headline number is exciting. The honest reading is that several things still need to settle before we know how retatrutide will land in real-world practice.

Gastrointestinal side effects rise with dose, as they do with all GLP-1 medication. Discontinuation rates at the higher trial doses ran somewhat higher than for placebo. Whether that is manageable with slower titration is one of the things the next year of trial readouts will tell us.

The 12mg dose has shown the best balance of effect and tolerability in trial. Whether real-world prescribing will use the same dose, or whether maintenance will sit at a lower level, is not yet settled.

Long-term safety is the question that always trails a new medication. The retatrutide trials have followed patients out to 104 weeks; the body of evidence for semaglutide and tirzepatide now runs to many years. We give retatrutide credit for what the trial data shows; we do not pretend the long view exists yet.

Where the medication is in the licensing journey

Phase 3 is the stage where a medication is tested at scale against placebo and against existing treatments. Eli Lilly has eight Phase 3 trials in the retatrutide programme; results have been coming through across late 2025 and 2026 and the remaining readouts are expected by the end of 2026.

After the trial programme completes, Eli Lilly submits the full data package to regulators. The MHRA review for a medication of this profile typically takes nine to twelve months from submission. None of this is guaranteed: regulators can request more data, the company can delay, the trial programme could turn up something that changes the picture. We will not predict a UK licensing date because honest medicine does not.

What we can say: progress through Phase 3 has been on schedule, the results so far have been strong, and Eli Lilly has clearly stated the intention to file with regulators including the MHRA. The pipeline is moving in the right direction.

What this means for you

If you are starting weight-management treatment now, the right answer is one of the three medications already licensed: Wegovy, Mounjaro or Rybelsus. They work, they are evidence-based, and they are available today. Putting off treatment for a medication that might or might not arrive in 12-24 months is not the right call.

If you are already in treatment and reading this with interest, the practical implication is that the next generation is in view. The medication you start on now may not be the medication you are still on three years from now. We design treatment plans to be flexible: dose, drug and route of administration can all change as the evidence and the options change.

If retatrutide is licensed by the MHRA, our position is straightforward. We will assess the licensed product, integrate it into our protocols, and offer it to patients for whom it is the right choice. There will be no waiting list at our end.

The honest summary

Retatrutide is the most exciting weight-loss medication on the horizon. The Phase 3 data so far justifies the attention. It is not licensed in the UK yet and we cannot promise when it will be. What we can promise is that we are watching the evidence closely, we will prescribe it the day the MHRA grants a licence, and in the meantime we will be straight with you about what is and is not available today.

[Begin your consultation](/services/weight-management/prepare) with our weight management doctors.

Ready to start?

If this article has made you think weight-loss treatment might be right for you, the next step is a short consultation with one of our weight-management doctors.

Begin your assessment at this link. Online in 30 minutes, or in person at Westfield London.